The present disclosure relates generally to mechanisms that safeguard hard disk drives (HDDs) in the event of unexpected power loss. While HDDs have been proven to be robust data storage devices, certain precautions may be needed to protect mechanical parts of the drive from damage. For example, contact between a read/write head and a magnetic disk can cause damage to the disk. During drive operation, read/write heads ride a thin layer of air that separates the heads from the disks as they are spinning. This enables the heads to be in close proximity to the media surface for reading and writing to the media without allowing the heads to touch the surface of the disk.
The spinning disks maintain this layer of air that the heads ride upon, and so the heads could touch the disk if the disks stop spinning. As a result the read/write heads are often “parked” as part of a power-down sequence of the drive. Parking generally involves moving the heads to a reserved location on the disk where no data are stored or unloading the heads on to a ramp. Parking is typically performed to prevent damage to the surface of the disk and to reduce the amount of torque needed to restart the disk spindle motor. A HDD device may also have provisions for parking the head upon unexpected loss of power. For example, a reserve source of power, such as a still-spinning disk spindle motor, may be used as a generator to provide enough power to retract an actuator that parks the read/write head.